zoukankan      html  css  js  c++  java
  • poj2109 Power of Cryptography

    Description

    Current work in cryptography involves (among other things) large prime numbers and computing powers of numbers among these primes. Work in this area has resulted in the practical use of results from number theory and other branches of mathematics once considered to be only of theoretical interest. 
    This problem involves the efficient computation of integer roots of numbers. 
    Given an integer n>=1 and an integer p>= 1 you have to write a program that determines the n th positive root of p. In this problem, given such integers n and p, p will always be of the form k to the nth. power, for an integer k (this integer is what your program must find).

    Input

    The input consists of a sequence of integer pairs n and p with each integer on a line by itself. For all such pairs 1<=n<= 200, 1<=p<10101 and there exists an integer k, 1<=k<=109 such that kn = p.

    Output

    For each integer pair n and p the value k should be printed, i.e., the number k such that k n =p.

    Sample Input

    2 16
    3 27
    7 4357186184021382204544

    Sample Output

    4
    3
    1234
    这题可以用double型做,

    类型            长度 (bit)           有效数字                   绝对值范围

        float            32                     6~7                 10^(-37) ~ 10^38

        double         64                    15~16              10^(-307) ~10^308

        long double  128                  18~19               10^(-4931) ~ 10 ^ 4932

    因为k^n=p,所以k=p^(1.0/n);

    #include<stdio.h> #include<math.h> int main() { double n,m; while(scanf("%lf%lf",&n,&m)!=EOF)     {     printf("%.0f ",pow(m,(1.0)/n));     }     return 0; }

    也可以用二分法做

    #include<stdio.h> #include<string.h> #include<math.h> #define eps 1e-8 int main() { double n,m,i,j,h,temp; int l,r,mid; while(scanf("%lf%lf",&n,&m)!=EOF) { r=1000000000; l=1; while(l<=r){ mid=(l+r)/2; temp=pow(mid,n); //printf("%lf       %lf ",temp,pow(mid,n)); if(fabs(pow(mid,n)-m)<eps){ printf("%d ",mid);break; //因为这里求的是一个确定的整数,所以可以直接输出 } else if(pow(mid,n)<m){ l=mid+1; } else if(pow(mid,n)>m){ r=mid-1; } } } return 0; }

  • 相关阅读:
    Windows设置多用户同时远程登录
    Scala配置环境变量windows
    Java学习|强引用,软引用,弱引用,幻想引用有什么区别?
    Java学习|Exception和Error有什么区别?
    关于异常处理的几点建议
    win Server 2008 笔记
    .Net 初步学习笔记之三---变量
    认识与入门 MarkDown 标记语言
    C# winform基础 1、Timer不起作用 2、 设置图片透明
    IIS启动失败,启动Windows Process Activation Service时,出现错误13:数据无效 ;HTTP 错误 401.2
  • 原文地址:https://www.cnblogs.com/herumw/p/9464824.html
Copyright © 2011-2022 走看看